Just so happens I found this message in my long ago mail stack.  It
explains DLT media life.  This was in response to a specific question so
never mind the pronouns.

Re. very old tapes.  With most software, the catalog of old tapes is long
gone anyway.  It would be very difficult to recreate what was on a tape.

Kelly


>The DLT tapes are spec'd at 500,000 passes.  Each backup will do a minimum
of
>64 passes.  Assuming the drive will not stream perfectly, you may have
>200-500 passes.  Based on this, the tape will should last 1000 backups.
>
>In general, the problem that usually occurs with DLT is not tape wear, but
>the tapes getting contaminated.  Using the above figures and your
specified
>use model, the tapes will last almost 40 years.  However in this timeframe
>the tapes will also be gathering environmental contaminants that can and
will
>effect their life.  We typically recommend using the tapes in a clean
>environment (stored in their plastic cases) for 2-3 years.  In a
relatively
>dirty environment, from 6mos to 2 years depending upon the na
>ture of the environment.  Also, if you are unable to consistently stream
the
>tape drives, it will prematurely wear the tapes.
>
>In summary, according to the specifications, the tapes will last 38.5
years
>assuming one backup every other week and 500 passes per backup.  Due to
>environmental concerns and unpredictable variables (ability to stream and
>number of passes required per backup) I would recommend retiring tapes
after
>2-3 years.
>